Letter Never Sent(1960)
Original Title: Неотправленное письмо
Four geologists are searching for diamonds in the wilderness of Siberia. After a long and tiresome journey they manage to find their luck and put the diamond mine on the map. The map must be delivered back to Moscow. But on the day of their departure a terrible forest fire wreaks havoc, and the geologists get trapped in the woods.
Letter Never Sent streaming: where to watch online?
Currently you are able to watch "Letter Never Sent" streaming on Criterion Channel.